In order to provide an optical switching function in an optical relay, optical fibres may be used which are mechanically moved in relation to each other so that light from an incoming fibre can be optionally switched to one of several alternative outgoing fibres. Several different solutions to such optical switching functions have been proposed such as shown, for example, in British Pat. No. 1,580,109 and in German Offenlegungsschrift No. 3,012,450.
The disadvantage of the prior is the magnitude of cost of handling the fibres in the provision of the switching function. The fibres must have their ends cut or ground flat and placed correctly within very narrow limits in relation to each other both axially and radially if optical attenuation is to be kept low.